Liquid crystal is a term that generally indicates the status of a substance that is neither solid nor liquid. Liquid crystal displays (LCDs) are categorized as non-emissive display devices, therefore they do not produce any form of light like a Cathode Ray Tube (CRT). LCDs either pass or block light that is reflected from an external light source or provided by a back/side lighting system.
FIG. 1 is a cross-section of a twisted nematic LCD panel in transmission mode. Liquid crystal material 5 is contained between two glass plates 10 and 15; each plate has microscopic grooves on its inner surface, with the grooves aligned at an angle to each other, typically 90°. The alignment of the plate grooves causes the molecule alignment of liquid crystal material 5 to spiral by 90° between the bottom and top of the panel. Light is projected through the panel, in this case, by backlight source 27. To obtain control of light transmission in the panel, two polarizers 20 and 25 are placed behind and above the panel, with their plane of polarization aligned with the grooves in the glass plates. As the light passes through liquid crystal material 5, its polarization is rotated as the molecule alignment twists, so that full light transmission occurs even though the polarizers are at 90° to each other.
An electric field is applied to a location on the panel by applying voltage to control electrodes 30 and 35. The electric field causes molecules 40 of liquid crystal material 5 to begin to align with the field and the 90° spiral is disrupted. The result is that as light transmission is reduced, the panel gets darker where the field is applied.
A flat panel display is formed of many pixels, e.g., 640 rows by 480 columns. Each pixel may be represented for monochromatic displays, as the panel illustrated in FIG. 1. For color applications, a pixel such as illustrated in FIG. 1 may be divided into sub-pixels such as Red, Green, and Blue sub-pixels with color filter material controlling the emitted light from each sub-pixel.
As shown in FIG. 2, current flat panel displays 45 are fabricated of semiconductor chip-like structures of thousands of devices, e.g., transistors, diodes, etc., formed on a single substrate. One problem is that each of the many panels of transistors and diodes have to meet a minimum performance standard and it is not always possible to determine if there is a defective element until the end of the process. Because of defective element 50 (e.g., defective pixels), production is lost and the whole batch must be discarded. Also, flat displays generally cannot be made very big and are difficult to produce.
A second type of display is a projection display requiring a projector. Front projection occurred if one was on the same side as the screen, whereas rear projection occurred if one was on one side of the screen and the projector was on another. One type of projector 55, as shown in FIG. 3, is the micro-mirror. Micro-mirror device 60 steers light in the desired spots as the color of light is changing, steering the light across sheet 65. One problem with micro-mirror devices is that there exists a significant gap between projector 55 and screen 65, particularly as the size of the screen increases. Reducing the gap between the projector and the screen creates distortion. Therefore, a balance must occur, that is, a balance to get close enough for a clear image but far enough to avoid any distortion, which can be difficult to accomplish.
The “picture on the wall” display has long been a goal of television (TV) display research. Numerous technologies have been developed but none has been commercially significant in the TV field except for small portable receivers where CRT displays are impractical. The entry for flat panels into the TV market may be HDTV, where large high-resolution displays are generally required. CRTs for this market are going to be expensive devices in the home and presents an opportunity for flat panels to get into the market provided such displays can achieve desired screen sizes at reasonable costs. It would also be desirable to have a flat panel display that is easier to build as it gets larger instead of being more difficult to build as it gets larger.
What is needed is a flat display that is easier to build as it gets larger instead of being more difficult to build as it gets larger. We also want to eliminate the need to front up rear projection.